The invention concerns a deactivating cam system for a valve train of an internal combustion engine, said cam system comprising a camshaft on which at least one cam is seated for rotation but fixed in axial direction while being able to be connected rotationally fast to the camshaft connected through a coupling device.
A factor of increasing importance in the designing and implementation of a variable valve train in an automotive vehicle is the design space requirement of the switchable valve train components because the design space in modern engines, typically comprising four valves per cylinder, is restricted. The design space problems are further aggravated through the increasing use of direct fuel injection systems. Another requirement is that the gear shifting forces for adjusting the valve train and for actuating the gas exchange valves must be as low as possible, so that wear in the valve train is kept to a low level. A shifting of the gear shifting function to the camshaft has proved to be a favorable solution.
U.S. Pat. No. 5,239,885 discloses a deactivating cam system in which a coupling device optionally enables a rotationally fast connection to be made or to be released between a camshaft and a cam arranged axially fixed thereon. The coupling device comprises a coupling pin which extends in a radial bore of the camshaft while being loaded by a compression spring, said coupling pin being supported through spring force in radial direction in a recess within the cam, so that the cam is coupled rotationally fast. The coupling pin is seated positively engaged in a conical seating region configured in the recess. Continuing from the coupling recess is configured a pressure chamber which can be pressurized with hydraulic medium through an axial pressure medium supply of the camshaft and through a connecting channel.
For uncoupling the cam, the pressure chamber is flooded with hydraulic medium, so that the increasing pressure acts in opposition to the spring force with the result that the coupling pin is pressed back out of the recess into the camshaft bore till relative movements between the camshaft and the cam are enabled which begin when the cam lobe reaches the associated cam follower in the course of the camshaft rotation. The cam follower is thus not loaded by an adjusting force, so that, as a result of this, the corresponding gas exchange valve remains closed.
Because the seating surfaces of the coupling pin and the recess absorb, during locking, the actuating forces and, in the coupled position, all the relative forces produced between the cam and the camshaft, the coupling device is relatively prone to wear and also exhibits large tolerances. A durable, unproblematic functioning can only be achieved with high manufacturing costs.